Minnesota Department of Transportation Office of Materials & Road Research 1400 Gervais Avenue, Maplewood, MN 55109 Memo An Equal Opportunity Employer DATE: October 1 st , 2018 TO: Mike Gerbensky, Project Manager Metro District FROM: Hossana Teklyes, Assist. Foundations Engineer Geotechnical Engineering Section Foundations Unit CONCUR: Derrick Dasenbrock, Geomechanics/LRFD Engineer Geotechnical Engineering Section Foundation Unit Paul Martin, Assistant Foundations Engineer Geotechnical Engineering Section Foundation Unit SUBJECT: S.P. 1901-184, Replace High Mast Tower Lighting Systems (Metro District) TH13 at JCT TH77 in Eagan Foundations Investigation and Recommendations Project Description This report provides a Foundation Analysis and Recommendations for constructing foundations for 12 new High Mast Light Towers (HMLTs) on TH13 at junction TH77 in Eagan. This report also provides a request to keep 3 tower bases intact for an active research project with the University of Minnesota as part of a cooperative effort with the Bridge Office to determine unknown pile lengths of HMLT installations for a future investigation/retrofit program. Field Investigation and Foundation Conditions Ten Cone Penetration Tests (CPT Soundings) and one Standard Penetration Test (SPT Borings) were taken by MnDOT in May of 2018 at the High Mast Light Tower foundation locations. One additional old boring taken in 1979 (TE8) for an old light tower near the location of light tower E8 was also used. The soils at the light tower locations predominantly consist of medium dense silty sand to dense sandy soil. Water was encountered 15 ft. below existing ground (elevation 778.6 ft.) in the one boring (T09) taken at the location of light tower E9. Copies of the CPT & SPT logs are attached with this report.
Transcript
Minnesota Department of Transportation Office of Materials & Road Research 1400 Gervais Avenue, Maplewood, MN 55109
Memo
An Equal Opportunity Employer
DATE: October 1st, 2018
TO: Mike Gerbensky, Project Manager Metro District
CONCUR: Derrick Dasenbrock, Geomechanics/LRFD Engineer Geotechnical Engineering Section Foundation Unit Paul Martin, Assistant Foundations Engineer Geotechnical Engineering Section Foundation Unit SUBJECT: S.P. 1901-184, Replace High Mast Tower Lighting Systems (Metro District) TH13 at JCT TH77 in Eagan Foundations Investigation and Recommendations Project Description This report provides a Foundation Analysis and Recommendations for constructing foundations for 12 new High Mast Light Towers (HMLTs) on TH13 at junction TH77 in Eagan. This report also provides a request to keep 3 tower bases intact for an active research project with the University of Minnesota as part of a cooperative effort with the Bridge Office to determine unknown pile lengths of HMLT installations for a future investigation/retrofit program. Field Investigation and Foundation Conditions Ten Cone Penetration Tests (CPT Soundings) and one Standard Penetration Test (SPT Borings) were taken by MnDOT in May of 2018 at the High Mast Light Tower foundation locations. One additional old boring taken in 1979 (TE8) for an old light tower near the location of light tower E8 was also used. The soils at the light tower locations predominantly consist of medium dense silty sand to dense sandy soil. Water was encountered 15 ft. below existing ground (elevation 778.6 ft.) in the one boring (T09) taken at the location of light tower E9. Copies of the CPT & SPT logs are attached with this report.
S.P.1901-184, TH13 @ JCT TH77, High Mast Light Towers Subsurface Investigation & Foundation Analysis October 1st, 2018
An Equal Opportunity Employer
Foundation Analysis The proposed light tower locations and ground elevations were provided by the Metro District. The proposed light towers will be 100 or 120 ft. in height. The HMLT Foundation Standard Design sheets, developed by the Bridge office in December of 2011, provide standard details for supporting light towers on spread footings. At this time, details for pile foundations are being developed by the Bridge office and will be available for use on this project. Review of Shallow Foundation Option The spread footing design option utilizes three different square footings depending on tower height and a minimum bottom of footing embedment of 5 ft. below existing ground. Table 1 below shows the minimum soil strength parameters for a minimum effective unit weight, friction angel and cohesion required for the standard spread footing foundation design. Table 1: Minimum soil strength parameters for Spread Footing (Standard Plans 5-297.321)
Soil Type Effective Unit Weight (pcf) Friction Angle (Φ) Cohesion (psf)
Sandy Soil 52.5 30 0
Clay Soil 57.5 0 1000
Pile Foundation Option The tower locations were also assessed for the use of 10x42 and 12-inch diameter CIP piles. Anticipated pile lengths were calculated to meet both compression and tension design requirements. Pile capacity was evaluated using the software Unipile. It is assumed that the project will be more cost effective if all tower foundation use the driven pile design because the tower base is smaller, requiring less excavation and concrete. The contractor will also have equipment and materials for installing piling at over half of the towers, so the additional work would not require significantly different mobilization or material shipping costs. Please contact our office if spread footing foundations are preferred for other project reasons. Table 2 below includes minimum pile depth requirement and type of foundation that can be used for the high mast light towers. A factored structural uplift requirement of 25 tons was used in our calculations, with a LRFD resistance factor of 0.3, for a Nominal geotechnical uplift resistance of 83 tons.
S.P.1901-184, TH13 @ JCT TH77, High Mast Light Towers Subsurface Investigation & Foundation Analysis October 1st, 2018
An Equal Opportunity Employer
Table 2: Summary of Foundation Recommendations for Light Towers.
Pole # Pole
height (ft.)
CPT Soundings or
Borings
Estimated Pile depth for Nominal
200 ton Compression
(ft.)
Required
Minimum Pile depth for
Nominal 83 ton Tension (Uplift)
(ft.)*
Estimated Pile embedment for
10x42 H-Pile for 200 ton Nominal
Bearing Capacity(ft.)*
Spread
Footing is an option at
this location**
C1 100 c01 35 35 40 Yes
C2 120 c02 20 25 30 No
C3 100 c03a 20 30 30 Yes
C4 120 c04 25 30 30 Yes
C5 100 c05 20 25 25 Yes
C6 100 c06c 10 25 25 Yes
C7 100 c07c 15 25 25 No
E8 120 TE-8 40 40 40 No
E9 120 T09 45 40 45 No
E10 100 c10 30 25 35 No
E11 100 c11 25 25 25 No
E12 100 c12c 35 25 35 No *The minimum required pile depth reflects the minimum length of pile below ground to satisfy the uplift requirement. Using the MPF 12 formula, piles could achieve 200 ton nominal capacity prior to this criterion. If 200 tons Nominal Bearing Resistance, using the MPF 12 formula, is not satisfied at this minimum tip elevation, then driving should continue until the bearing resistance is achieved. **Tower locations C2, C7, E8, E9, E10, E11, and E12 are not suitable for the standard spread footing design. A project specific set of pile design sheets will be required where piling is driven; refer to the recommendations section (piling can be used for all HMLT foundations, as rock was not encountered). HMLT Unknown Pile Length and Pile Uplift Research As part of the cooperative project between the Bridge Office and the Office of Materials & Road Research to potentially retrofit existing towers, several sites are needed to study techniques for determining unknown pile lengths. As part of this work, it is desirable to have 3 light tower bases remain above grade (with the towers and power systems removed) for use in testing various methods. We are interested, as part of this contract, in preserving 3 intact pile-supported tower foundations which are easily accessible, but sufficiently far or protected from traffic so as not to be a safety hazard during the testing
S.P.1901-184, TH13 @ JCT TH77, High Mast Light Towers Subsurface Investigation & Foundation Analysis October 1st, 2018
An Equal Opportunity Employer
and research work, or accessing the towers. After the multi-year instrumentation study and as part of a future contract project, the selected tower foundations would be abandoned similarly to the methods called for in this plan where the top collars are removed and turf established. The anticipated impact to this project would be a slight reduction in the amount of work for tower base removal. The preferred tower locations are at in-place towers T2C T1, T2C T2 and T2E T10. Refer to Figures 1-3 for the tower site conditions and Figure 4 for a map showing the selected locations.
Figure 1: T2C T1 is located off of MN 77 and is behind protective guardrail with good CPT truck access.
Figure 2: T2C T2 is located in the SE cloverleaf ramp with good sight distances and CPT truck access. This is the deepest existing foundation at the site and different than the estimated depths of the other two towers, making it a preferred location.
T2C T2
T2C T1
S.P.1901-184, TH13 @ JCT TH77, High Mast Light Towers Subsurface Investigation & Foundation Analysis October 1st, 2018
An Equal Opportunity Employer
Figure 3: T2E T10 is the most preferred location, from an access and safety perspective; it is along MN 13, where traffic is lighter and the location is well off both the mainline and the ramp. The ground is relatively flat for good CPT truck access. The towers have been selected for safety, access with a CPT truck rig, and length of foundation piling. The proposed new tower locations are 242 feet from tower T2C T1, 45 feet from tower T2C T2 and 71 feet from tower T2E T10, which should allow adequate space for new towers to be installed without conflicting with the existing foundations. The proposed geotechnical monitoring and instrumentation work will not be concurrent with the project; as such, no delays to the HMLT project work or cost are anticipated.
T2E T10
S.P.1901-184, TH13 @ JCT TH77, High Mast Light Towers Subsurface Investigation & Foundation Analysis October 1st, 2018
An Equal Opportunity Employer
Figure 4: Selected HMLT bases for preservation (remaining in place after towers are removed). Recommendations Based on the existing conditions along with an analysis of the project soils, we recommend:
1. Support the HMLT foundations using 10x42 driven H-pile foundations as described in the following recommendations using driven pile foundations for all towers.
2. Contact the Bridge Office for a project specific footing design sheet; a standard plan is not available
for HMLT founded on piling at this time.
3. Provide piling with the minimum required embedment (tip depth) of piling as shown in Table 3 and repeated in Table 5 in the plan sheet format (below) for the piles supporting the HMLT structures. The minimum embedment requirement is to ensure that driven piles have a sufficient embedded length to provide the required uplift resistance. When developing the plan drawings or associated special provisions (if not shown on the plans), provide minimum pile tip embedment as described in
T2E T10
T2C T2
T2C T1
S.P.1901-184, TH13 @ JCT TH77, High Mast Light Towers Subsurface Investigation & Foundation Analysis October 1st, 2018
An Equal Opportunity Employer
Table 3 to ensure adequate uplift capacity. The piles may need to be driven beyond the minimum tip depth to satisfy the Nominal Geotechnical Bearing requirement of 200 tons. Table 3: Summary of Foundation Recommendations for Light Towers.
Pole # Pole height (feet)
Minimum Pile Embedment for Uplift(Tension) Design 10x42 H-
Pile
Nominal
Geotechnical Bearing
(MPF 12)
C1 100 35
167 tons
C2 120 25
C3 100 30
C4 120 30
C5 100 25
C6 100 25
C7 100 25
E8 120 40
E9 120 40
E10 100 25
E11 100 25
E12 100 25
4. Use the MnDOT dynamic pile driving formula, MPF12, as the pile driving construction control
method. Use the required loads in the Pile Bearing Resistance Table on the standard plan. As this project uses only H-type piles, the information for CIP piles may be crosses out as shown below with an “X” for items not used in this project.
S.P.1901-184, TH13 @ JCT TH77, High Mast Light Towers Subsurface Investigation & Foundation Analysis October 1st, 2018
An Equal Opportunity Employer
5. Include the following information in the “PILE TABLE” located on the HMLT plan sheet as follows:
Tower No. Type of Pile
Bottom of Footing
Elevation* (ft.)
Estimated Length (ft)
Required Min. Pile
Length (ft.)
Actual Driven Length of Each
Pile**
C1 H 10x42 [See plan*] 40 35 . .
C2 H 10x42 [See plan*] 30 25 . .
C3 H 10x42 [See plan*] 30 30 . .
C4 H 10x42 [See plan*] 30 30 . .
C5 H 10x42 [See plan*] 25 25 . .
C6 H 10x42 [See plan*] 25 25 . .
C7 H 10x42 [See plan*] 25 25 . .
E8 H 10x42 [See plan*] 40 40 . .
E9 H 10x42 [See plan*] 45 40 . .
E10 H 10x42 [See plan*] 35 25 . .
E11 H 10x42 [See plan*] 25 25 . .
E12 H 10x42 [See plan*] 35 25 . .
*Designer to establish this value based on the project specific plan locations of the towers and proposed final project grading. **This column to be filled in by contractor with as-built information for submittal to the Bridge Office for transportation asset management.
Information is this table is site specific and is not applicable
Recommendations continue on next page
S.P.1901-184, TH13 @ JCT TH77, High Mast Light Towers Subsurface Investigation & Foundation Analysis October 1st, 2018
An Equal Opportunity Employer
For this project: As an aid to the unknown foundation length research project (driven piling):
6. Develop contract plans and special provisions to allow for 3 intact foundations to remain in-place
above ground. After removing the light tower steel structure, leave the complete concrete foundations intact (including anchor assemblies) at existing towers T2C T1, T2C T2 and T2E T10. A future contract will include removal of the above ground concrete portion of the towers and restoration of vegetation when the HMLT research is complete and a project to determine unknown tower lengths in the metro district is established.
If you have any additional questions regarding these recommendations, or require further assistance, please contact this office. Attachments: Boring/Sounding Plan CPT Index Sheet CPT Sounding Logs (C01 – C12c) (MnDOT Unique Numbers 83094 - 83122) SPT Index Sheet SPT Boring Logs (T09 & TE-8) (MnDOT Unique Numbers 83116 & 51284) cc: B. Skow T. Clyne
Minnesota Department of Transportation Geotechnical Section
Cone Penetration Test Index Sheet 1.0 (CPT 1.0)
USER NOTES, ABBREVIATIONS AND DEFINITIONS This Index sheet accompanies Cone Penetration Test Data. Please refer to the Boring Log Descriptive Terminology Sheet for information relevant to conventional boring logs. This Cone Penetration Test (CPT) Sounding follows ASTM D 5778 and was made by ordinary and conventional methods and with care deemed adequate for the Department's design purposes. Since this sounding was not taken to gather information relating to the construction of the project, the data noted in the field and recorded may not necessarily be the same as that which a contractor would desire. While the Department believes that the information as to the conditions and materials reported is accurate, it does not warrant that the information is necessarily complete. This information has been edited or abridged and may not reveal all the information which might be useful or of interest to the contractor. Consequently, the Department will make available at its offices, the field logs relating to this sounding. Since subsurface conditions outside each CPT Sounding are unknown, and soil, rock and water conditions cannot be relied upon to be consistent or uniform, no warrant is made that conditions adjacent to this sounding will necessarily be the same as or similar to those shown on this log. Furthermore, the Department will not be responsible for any interpretations, assumptions, projections or interpolations made by contractors, or other users of this log. Water pressure measurements and subsequent interpreted water levels shown on this log should be used with discretion since they represent dynamic conditions. Dynamic Pore water pressure measurements may deviate substantially from hydrostatic conditions, especially in cohesive soils. In cohesive soils, water pressures often take extended periods of time to reach equilibrium and thus reflect their true field level. Water levels can be expected to vary both seasonally and yearly. The absence of notations on this log regarding water does not necessarily mean that this boring was dry or that the contractor will not encounter subsurface water during the course of construction. CPT Terminology CPT .............Cone Penetration Test CPTU...........Cone Penetration Test with Pore Pressure measurements SCPTU.........Cone Penetration Test with Pore Pressure and Seismic measurements Piezocone...Common name for CPTU test (Note: This test is not related to the Dynamic Cone Penetrometer DCP) qT TIP RESISTANCE The resistance at the cone corrected for water pressure. Data is from cone with 60 degree apex angle and a 10 cm2 end area. fs SLEEVE FRICTION RESISTANCE The resistance along the sleeve of the penetrometer. FR Friction Ratio
Ratio of sleeve friction over corrected tip resistance. FR = fs/qt Vs Shear Wave Velocity A measure of the speed at which a siesmic wave travels through soil/rock. PORE WATER MEASUREMENTS Pore water measurements reported on CPT Log are representative of water pressures measured at the U2 location, just behind the cone tip, prior to the sleeve, as shown in the figure below. These measurements are considered to be dynamic water pressures due to the local disturbance caused by the cone tip. Dynamic water pressure decay and Static water pressure measurements are reported on a Pore Water Pressure Dissipation Graph.
SBT SOIL BEHAVIOR TYPE Soil Classification methods for the Cone Penetration Test are based on correlation charts developed from observations of CPT data and conventional borings. Please note that these classification charts are meant to provide a guide to Soil Behavior Type and should not be used to infer a soil classification based on grain size distribution. The numbers corresponding to different regions on the charts represent the following soil behavior types: 1. Sensitive, Fine Grained 2. Organic Soils - Peats 3. Clays - Clay to Silty Clay 4. Silt Mixtures - Clayey Silt to Silty Clay 5. Sand Mixtures - Silty Sand to Sandy Silt 6. Sands - Clean Sand to Silty Sand 7. Gravelly Sand to Sand 8. Very Stiff Sand to Clayey Sand 9. Very Stiff, Fine Grained Note that engineering judgment, and comparison with conventional borings is especially important in the proper interpretation of CPT data in certain geo-materials. The following charts are used to provide a Soil Behavior Type for the CPT Data. Robertson CPT 1990 Soil Behavior type based on friction ratio
Robertson CPTU 1990 Soil Behavior type based on pore pressure
U2
where ... QT.......................... normalized cone resistance Bq.......................... pore pressure ratio Fr ........................... Normalized friction ratio σvo ........................ overburden pressure σ’vo ....................... effective over burden pressure u2 .......................... measured pore pressure u0 .......................... equilibrium pore pressure G:\GEOTECH\PUBLIC\FORMS\CPTINDEX.DOC January 30, 2002
End of Data
Bottom of Hole 35.5,Planned Depth
State Project
LIGHTING BASEBridge No. or Job Desc.
Tip Resistance(psi)UBC 1990 FR
Pore Pressure(psi)
Depth
Sounding No.
Elevation
Ground Elevation
c01Trunk Highway/Location
(DTM)TH 13 / TH 771901-184
Friction Ratio(%)
Interpreted SoilBehavior Type Sleeve Friction
(psi)
830.5Location CPT Machine
5/23/18
ODonnel
SHEET 1 of 1
CPT-STD
203094 CPT Truck
Latitude (North)=44°48'39.65"
(ft.)
No Station-Offset Information Available
Longitude (West)=93°13'07.69" CPT Operator
Hole Type
Date Completed
Index Sheet Code 3.0
Dakota Co. Coordinate: X=525400 Y=223639
MINNESOTA DEPARTMENT OF TRANSPORTATION - GEOTECHNICAL SECTION
USER NOTES, ABBREVIATIONS AND DEFINITIONS - Additional information available in Geotechnical Manual. This boring was made by ordinary and conventional methods and with care deemed adequate for the Department's design purposes. Since this boring was not taken to gather information relating to the construction of the project, the data noted in the field and recorded may not necessarily be the same as that which a contractor would desire. While the Department believes that the information as to the conditions and materials reported is accurate, it does not warrant that the information is necessarily complete. This information has been edited or abridged and may not reveal all the information which might be useful or of interest to the contractor. Consequently, the Department will make available at its offices, the field logs relating to this boring. Since subsurface conditions outside each borehole are unknown, and soil, rock and water conditions cannot be relied upon to be consistent or uniform, no warrant is made that conditions adjacent to this boring will necessarily be the same as or similar to those shown on this log. Furthermore, the Department will not be responsible for any interpretations, assumptions, projections or interpolations made by contractors, or other users of this log. Water levels recorded on this log should be used with discretion since the use of drilling fluids in borings may seriously distort the true field conditions. Also, water levels in cohesive soils often take extended periods of time to reach equilibrium and thus reflect their true field level. Water levels can be expected to vary both seasonally and yearly. The absence of notations on this log regarding water does not necessarily mean that this boring was dry or that the contractor will not encounter subsurface water during the course of construction. WATER MEASUREMENT
Augered Plug Drilled Split Tube Sample (SPT N60 2 in. spilt tube with liners) Thin Wall Sample (3 in. Shelby Tube) Core Drilled (NV Core Barrel unless otherwise noted) Continuous Soil Sample Augered & Jetted Jetted Augered & Plug Drilled
WS
PD
CS
A/J Jet A/P
AB ........................ After Bailing AC ........................ After Completion AF......................... After Flushing w/C ....................... with Casing
Index Sheet No. 3.0 March 2003 G:\geotech\Public\Forms\INDEX30.doc
w/M ...................... with Mud WSD ..................... While Sampling/Drilling w/AUG.................. with Hollow Stem Auger MISCELLANEOUS NA ........................ Not Applicable w/ ......................... with w/o ....................... with out sat ........................ saturated DRILLING OPERATIONS AUG ................. Augered CD .................... Core Drilled DBD.................. Disturbed by Drilling DBJ .................. Disturbed by Jetting PD .................... Plug Drilled ST..................... Split Tube (SPT test) TW.................... Thinwall (Shelby Tube) WS.................... Wash Sample NSR.................. No Sample Retrieved
WH ................... Weight of Hammer WR ................... Weight of Rod Mud.................. Drilling Fluids in Sample CS .................... Continuous Sample SOIL/CORE TESTS SPT N60 ............ ASTM D1586 Modified Blows per foot with 140 lb. hammer and a standard energy of 210 ft-lbs. This energy represents 60% of the potential energy of the system and is the average energy provided by a Rope & Cathead system. MC.................... Moisture Content COH ................. Cohesion γ ....................... Sample Density LL..................... Liquid Limit PI...................... Plasticity Index Φ ...................... Phi Angle REC.................. Percent Core Recovered RQD ................. Rock Quality Description (Percent of total core interval consisting of unbroken pieces 4 inches or longer) ACL .................. Average Core Length (Average length of core that is greater than 4 inches long) Core Breaks .... Number of natural core breaks per 2-foot interval. DISCONTINUITY SPACING Fractures Distance Bedding Very Close........ <2 inches ............Very Thin Close ................ 2-12 inches .........Thin Mod. Close ....... 12-36 inches .......Medium Wide................. >36 inches ..........Thick DRILLING SYMBOLS
RELATIVE DENSITY Compactness - Granular Soils BPF
very loose....................................0-4 loose ...........................................5-10 medium dense ............................11-24 dense ..........................................25-50 very dense...................................>50
Consistency - Cohesive Soils BPF
very soft.......................................0-1 soft ..............................................2-4 firm ..............................................5-8 stiff ..............................................9-15 very stiff.......................................16-30 hard.............................................31-60 very hard .....................................> 60
COLOR blk .................. Black wht ...........White grn ................. Green brn............Brown orng ............... Orange yel.............Yellow dk ................... Dark lt ...............Light IOS ................. Iron Oxide Stained GRAIN SIZE /PLASTICITY VF............. Very Fine pl ............Plastic F ............... Fine slpl .........Slightly Cr ............. Coarse Plastic SOIL/ROCK TERMS C............... Clay Lmst .......Limestone L ............... Loam Sst ..........Sandstone S............... Sand Dolo........Dolostone Si.............. Silt wx...........weathered G .............. Gravel (No. 10 Sieve to 3 inches) Bldr .......... Boulder (over 3 inches) T ............... till (unsorted, nonstratified glacial deposits) Mn/DOT Triangular Textural Soil Classification System
100%
100%
C
90807060 50 40 302010
90
80
70
60
50
40
30
20
10
(plastic)
(slightly plastic)
SC
SCL CL
L SL SiL
Si
SiCL
LSS Si
90
80
70
60
50
40
30
20
10
100 %
% Sand % Clay
% Silt
5.0788.6
10.0783.6
13.7779.9
38.0755.6
41.5752.1
49.5744.1
4
5
18
13
14
118
12
12
13
12
21
13
11
Fine Sand with a little Gravel, dark-brown to brown, damp,medium dense
plastic to slightly plastic very fine grained Sandy Loam with highSilt content, brown, moist, very stiff to hard
Clay Loam with a few pebbles, gray, moist, very stiff to hard
slightly plastic to plastic fine grained Sandy Loam with pebbles,browns, moist to saturated, hard
Silty Clay Loam, gray, wet, hard
slightly plastic Sandy Loam, brown to gray, wet, very stiff
Bottom of Hole -49.5'Water measured at 14.9' with auger
